The present invention relates to an electromagnetic relay using a permanent magnet.
Various types of electromagnetic relays using permanent electromagnets are known. FIGS. 1 and 2 show one such conventional electromagnetic relay. Referring to these figures, holding portions 12 and 13 are formed at a predetermined distance on a substrate 11. Proximal ends 141 and 151 of movable contact pieces 14 and 15 extend through the holding portion 12 to be held thereby. Similarly, proximal ends 161 and 171 of movable contact pieces 16 and 17 extend through the holding portion 13 to be held thereby. Movable contacts 142 and 152 are formed on the pair of movable contact pieces 14 and 15 to oppose each other. Similarly, movable contacts 162 and 172 are formed on the pair of movable contact pieces 16 and 17 to oppose each other. Stationary contacts 18 and 19 are arranged at predetermined distances between the corresponding pairs of contacts 142 and 152 and of contacts 162 and 172, respectively. The stationary contacts 18 and 19 are arranged on terminals 181 and 191, respectively, proximal ends whereof extend through a holding portion 20 formed on the substrate 11.
A pivotal plate 21 is mounted on the substrate 11. The pivotal plate 21 comprises an arm 211 and a leg 212, forming an overall T shape. A through hole 213 is formed at the center of the pivotal plate 21 and receives a pin 22 extending upright from the substrate 11. Therefore, the pivotal plate 21 is pivotal about the pin 22 in the direction indicated by arrows A and B. A movable member 23 is mounted at the distal end of the leg 212. The movable member 23 comprises a permanent magnet 24 and iron pieces 25 and 26 whose proximal ends abut against the poles of the permanent magnet 24. Projections 214 and 215 are formed on two ends, respectively, of the arm 211. The projections 214 and 215 are respectively located between the movable contact pieces 14 and 15 and the movable contact pieces 16 and 17. As the pivotal plate 21 pivots, the projections 214 and 215 drive the movable contact pieces 14 and 15 and the movable contact pieces 16 and 17, respectively.
A substantially E-shaped iron core 27 constituting an electromagnet is arranged above the pivotal plate 21. The iron core 27 comprises a central portion 271 and first and second side portions 272 and 273. A coil 28 is mounted on the central portion 271. The iron core 27 having such a structure is fitted in and held by steps 121, 131 and 201 formed in the holding portions 12, 13 and 20. In the held state of the iron core 27, the distal ends of the iron pieces 25 and 26 of the movable member 23 are respectively located between the central portion 271 and the first and second side portions 272 and 273 of the iron core 27.
In the electromagnetic relay of the structure as described above, when the coil 28 is energized to magnetize the central portion 271 of the iron core 27 to the S pole, for example, and the first and second side portions 272 and 273 to the N pole, the iron pieces 25 and 26 magnetized to the S and N poles, respectively, by the permanent magnet 24 are attracted toward the first side portion 272 and the central portion 271, respectively. As a result, the pivotal plate 21 pivots about the pin 22 in the direction of arrow A, and this state is maintained even after the coil 28 is deenergized. When the coil 28 is energized in the direction opposite to that described above, the pivotal plate 21 is pivoted in the direction indicated by arrow B. The pivotal plate 21 operates in this manner so as to change the contact states of the contacts 142 to 172 of the movable contact pieces 14 to 17 and the stationary contacts 18 and 19.
The electromagnetic relay having the above structure can provide a necessary function as an electromagnetic relay. However, in this conventional electromagnetic relay, the movable member 23 is subject to a magnetic field acting in the direction perpendicular to the axis of the central portion 271 of the iron core 27, and tends to move linearly along this direction. However, in practice, the pivotal plate 21 pivots about the pin 22. For this reason, friction is generated between the pivotal plate 21 and the pin 22, so that the magnetic field acting on the movable member 23 may not be efficiently transmitted to the pivotal plate 21.
The friction generated between the pivotal plate 21 and the pin 22 and between the movable contact pieces 14 to 17 and the projections 214 and 215 changes in accordance with the posture of the relay mounted on a printed circuit board or the like. Accordingly, it is difficult to improve the sensitivity (power consumed by the coil for driving the same contact mechanism; smaller power means better sensitivity) of the relay. Moreover, the sensitivity of the relay varies in accordance with the posture of the relay.
The central portion 271 and the first and second side portions 272 and 273 of the iron core 27 are elongated, resulting in long magnetic paths and hence, relatively great magnetic reluctance. Then, the magnetic flux generated by the permanent magnet 24 may not be easily shielded and may permeate through the first and second side portions 272 and 273. The magnetic flux then leaks to the outside through a casing (not shown) and the substrate 11. In particular, leakage flux is easily caused in the direction perpendicular to the plane of the substrate 11. Therefore, nearby arrangement of another electromagnetic relay or the like in this direction may adversely affect the operation characteristics thereof.
Since the iron core 27 has the central portion 271 and the first and second side portions 272 and 273 arranged in the transverse direction, the overall width is considerably great. Accordingly, it is difficult to produce a compact electromagnetic relay.